This program includes the cooperative activity of three groups working on problems of Cell Division, Differentiation and Motility. The group of D. Mazia proposes projects on: the tracing of the first steps of the initiation of chromosome replication from surface changes to the initiation of DNA synthesis; the roles of nuclear and cytoplasmic components in the establishment of the mitotic apparatus. The group of F. Wilt proposes to investigate in depth the properties and activities of mRNAs stored in the cytoplasm of the ovum, focussing on the problem of the translational regulation of protein synthesis in differentiation. These studies will concentrate on histone mRNAs and polyadenylated mRNAs of the sea urchin egg and will use the Xenopus egg as a test system for translation. Studies on the role of oocyte cytoplasmic proteins in the structure and function of chromatin of early embryonic blastomeres will be carried out. The group of R.C. Strohman will work on the growth and development of muscle in the culture system, investigating the relation between the differentiation of myoblasts and the activation of myofibrillar myosin synthesis; relations between transcription and translation in differentiation; the characterization of the myosins; the relations between myosin synthesis and the contractile activity of the differentiating muscle; the modification of muscle differentiation by fusion of the cells with non-muscle cells. The program is designed for collaboration among the groups at points of interaction of problems and techniques and for the joint use of facilities.